1. Field of the Invention
The present invention relates to a pump which conveys a supercritical fluid or a liquid.
2. Description of the Prior Art
As one example of a pump which conveys a supercritical carbon dioxide (CO2) fluid or a liquid carbon dioxide, there is a circulation pump for cleaning the semiconductors. Along with high integration of the semiconductor devices in recent years, it is sought to have the wafers processed so as to be fine and minute in width. Therefore, against the present mainstream width of a wafer which is 0.18 μm, it is expected that the width thereof will be 0.10 μm or less. However, in the semiconductor-cleaning method which uses a conventional liquid such as extra-pure water and the like, when the wafer is dried, there is a case where such a phenomenon occurs as a resist being formed to the wafer is destroyed (“resist collapse”) by the capillary force which is caused by the boundary tension between the gaseous body and the liquid.
In order to eliminate the above-mentioned disadvantage, is developed a semiconductor-cleaning equipment which uses a supercritical fluid, instead of the conventional liquid such as extra-pure water. Compared with a liquid, the supercritical fluid has a very high permeability and can interpenetrate into any microscopic structure. In addition, because there exists no interface between the gaseous body and the liquid, it has such a characteristic as the capillary force does not work at the dime of drying.
As the supercritical fluid, mainly carbon dioxide (CO2) is used. Compared with other liquid vehicles, the carbon dioxide has a critical density of 468 kg/m3 on relatively moderate conditions, namely, that the critical temperature is 31.2° C. and the critical pressure is 7.38 Mpa. Furthermore, because the carbon dioxide is a gaseous body at a normal temperature and at normal pressures, it is gasified by returning the temperature and the pressure to be normal so that it is easy to separate an object to be cleaned from a contaminator. As a result, it will become unnecessary to dry the object to be cleaned after cleaning and the like, thereby making it possible to simplify the cleaning process and to reduce costs.
In such a semiconductor-cleaning equipment which uses a supercritical CO2 fluid as mentioned above, the supercritical CO2 fluid is generally pressurized to be approximately 20 Mpa. Therefore, so-called “having-no-seals” canned motor pump type is used, which has high pressure-tightness and produces a small number of particles, as a circulation pump for cleaning of the wafers by circulating the supercritical CO2 fluid. Additionally, ball bearings are used for bearings, which are used in the fluid serving as a cleaning agent of semiconductors (supercritical CO2 fluid).
The above-mentioned ball bearings receive the radial load and thrust load, which act on a rotor. Additionally, the preload is controlled by a preload spring which is installed to the bearing on the axial end side, being opposite to a bearing on the impeller side, which will be described later, and thereby so-called revolution skidding (side skidding) of a ball bearing is prevented. Moreover, rigidity (spring constant) in the radial direction of a ball bearing is controlled by the preload of the bearing, thereby adjusting the natural vibration frequency of the rotor.
As for the rest, is disclosed a canned motor pump which has a filter for capturing particles mounted in the fluid-introduction passageway. (For example, refer to the official bulletin of the Japanese Patent Application Laid-Open No. H11-324971.) By this, solid particles being included in the fluid are captured by the filter, so that the fluid containing no solid particles will be introduced into the inside of the motor. As a result, the fluid can flow smoothly in a narrow gap between the bearings of the motor portion or between the cans and the like, thereby being able to perform cooling and lubrication without damaging these members.
Or else, is disclosed a pump having a construction that integrates a fluid machinery which is driven by a driving machine; flow-volume-control means which control the flow volume of the handled fluid flowing inside the fluid machinery; activating means which operate the flow-volume-control means; and revolution-speed-control means which control the revolution speed of the driving machinery. (For example, refer to the official bulletin of the Japanese Patent Application Laid-Open No. 2003-56469.) By this, it is possible to integrate the fluid machinery, the revolution-speed-control system and the flow-volume-control system as one package. As a result, it is possible to simplify the installation work of the fluid machinery, thereby achieving labor-saving and natural-resources-saving.
However, in the future semiconductor-cleaning equipment, in order to enhance the cleaning ability of the wafers, it is necessary to increase the conveying flow volume of the fluid serving as a cleaning agent. Therefore, a pump for conveying the fluid is required to have a higher capacity. On the other hand, in order to save the space of the semiconductor-cleaning equipment, it is necessary to downsize the pump further. Therefore, contradictory requirements for a pump for cleaning the semiconductors, in other words, larger capacity and smaller size of the pump, must be satisfied.